Method and apparatus for monitoring a radio link on a small cell in a wireless communication system

ABSTRACT

A method and apparatus are disclosed for monitoring a radio link on a small cell in a wireless communication system. The method includes the UE receives a RRC message for configuring a second cell to the UE. The method also includes the UE transmits a complete message in response to the RRC message for configuring the second cell. The method further includes the UE monitors a radio link with the second cell and reports a radio link failure to the first eNB when the radio link failure is detected on the second cell, if the second cell is controlled by a second eNB. In one embodiment, the method includes (i) the UE stops uplink transmission(s) to the second cell after detection of the radio link failure, and/or (ii) the UE deactivates the second cell after detection of the radio link failure.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present Application claims the benefit of U.S. Provisional Patent Application Ser. No. 61/807,103 filed on Apr. 1, 2013, the entire disclosure of which is incorporated herein by reference.

FIELD

This disclosure generally relates to wireless communication networks, and more particularly, to a method and apparatus for monitoring a radio link on a small cell in a wireless communication system.

BACKGROUND

With the rapid rise in demand for communication of large amounts of data to and from mobile communication devices, traditional mobile voice communication networks are evolving into networks that communicate with Internet Protocol (IP) data packets. Such IP data packet communication can provide users of mobile communication devices with voice over IP, multimedia, multicast and on-demand communication services.

An exemplary network structure for which standardization is currently taking place is an Evolved Universal Terrestrial Radio Access Network (E-UTRAN). The E-UTRAN system can provide high data throughput in order to realize the above-noted voice over IP and multimedia services. The E-UTRAN system's standardization work is currently being performed by the 3GPP standards organization. Accordingly, changes to the current body of 3GPP standard are currently being submitted and considered to evolve and finalize the 3GPP standard.

SUMMARY

A method and apparatus are disclosed for monitoring a radio link on a small cell in a wireless communication system. The method includes the UE (User Equipment) receives a RRC (Radio Resource Control) message for configuring a second cell to the UE. The method also includes UE transmits a complete message in response to the RRC message for configuring the second cell. The method further includes the UE monitors a radio link with the second cell and reports a radio link failure to the first eNB (evolved Node B) when the radio link failure is detected on the second cell, if the second cell is controlled by a second eNB. In one embodiment, the method includes (i) the UE stops uplink transmission(s) to the second cell after detection of the radio link failure, and/or (ii) the UE deactivates the second cell after detection of the radio link failure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a diagram of a wireless communication system according to one exemplary embodiment.

FIG. 2 is a block diagram of a transmitter system (also known as access network) and a receiver system (also known as user equipment or UE) according to one exemplary embodiment.

FIG. 3 is a functional block diagram of a communication system according to one exemplary embodiment.

FIG. 4 is a functional block diagram of the program code of FIG. 3 according to one exemplary embodiment.

FIG. 5 illustrates a flow chart according to one exemplary embodiment.

FIG. 6 illustrates a flow chart according to one exemplary embodiment.

DETAILED DESCRIPTION

The exemplary wireless communication systems and devices described below employ a wireless communication system, supporting a broadcast service. Wireless communication systems are widely deployed to provide various types of communication such as voice, data, and so on. These systems may be based on code division multiple access (CDMA), time division multiple access (TDMA), orthogonal frequency division multiple access (OFDMA), 3GPP LTE (Long Term Evolution) wireless access, 3GPP LTE-A or LTE-Advanced (Long Term Evolution Advanced), 3GPP2 UMB (Ultra Mobile Broadband), WiMax, or some other modulation techniques.

In particular, the exemplary wireless communication systems devices described below may be designed to support one or more standards such as the standard offered by a consortium named “3rd Generation Partnership Project” referred to herein as 3GPP, including Document Nos. 3GPP TS 36.321 V11.2.0 (March 2013), “E-UTRA; MAC protocol specification”; TR36.392 v12.0.0 (December 2012), “Scenarios and Requirements for Small Cell Enhancements for E-UTRA and E-UTRAN”; RP-122033, “New Study Item Description: Small Cell enhancements for E-UTRA and E-UTRAN—Higher-layer aspects”; TS 36.300 V11.4.0 (December 2012), “E-UTRAN; Overall description; Stage 2”; TS 36.331 V11.3.0 (March 2013), “E-UTRA; RRC protocol specification”; and R2-110679, “Report of 3GPP TSG RAN WG2 meeting #72”. The standards and documents listed above are hereby expressly incorporated herein.

FIG. 1 shows a multiple access wireless communication system according to one embodiment of the invention. An access network 100 (AN) includes multiple antenna groups, one including 104 and 106, another including 108 and 110, and an additional including 112 and 114. In FIG. 1, only two antennas are shown for each antenna group, however, more or fewer antennas may be utilized for each antenna group. Access terminal 116 (AT) is in communication with antennas 112 and 114, where antennas 112 and 114 transmit information to access terminal 116 over forward link 120 and receive information from access terminal 116 over reverse link 118. Access terminal (AT) 122 is in communication with antennas 106 and 108, where antennas 106 and 108 transmit information to access terminal (AT) 122 over forward link 126 and receive information from access terminal (AT) 122 over reverse link 124. In a FDD system, communication links 118, 120, 124 and 126 may use different frequency for communication. For example, forward link 120 may use a different frequency then that used by reverse link 118.

Each group of antennas and/or the area in which they are designed to communicate is often referred to as a sector of the access network. In the embodiment, antenna groups each are designed to communicate to access terminals in a sector of the areas covered by access network 100.

In communication over forward links 120 and 126, the transmitting antennas of access network 100 may utilize beamforming in order to improve the signal-to-noise ratio of forward links for the different access terminals 116 and 122. Also, an access network using beamforming to transmit to access terminals scattered randomly through its coverage causes less interference to access terminals in neighboring cells than an access network transmitting through a single antenna to all its access terminals.

An access network (AN) may be a fixed station or base station used for communicating with the terminals and may also be referred to as an access point, a Node B, a base station, an enhanced base station, an eNodeB, or some other terminology. An access terminal (AT) may also be called user equipment (UE), a wireless communication device, terminal, access terminal or some other terminology.

FIG. 2 is a simplified block diagram of an embodiment of a transmitter system 210 (also known as the access network) and a receiver system 250 (also known as access terminal (AT) or user equipment (UE)) in a MIMO system 200. At the transmitter system 210, traffic data for a number of data streams is provided from a data source 212 to a transmit (TX) data processor 214.

In one embodiment, each data stream is transmitted over a respective transmit antenna. TX data processor 214 formats, codes, and interleaves the traffic data for each data stream based on a particular coding scheme selected for that data stream to provide coded data.

The coded data for each data stream may be multiplexed with pilot data using OFDM techniques. The pilot data is typically a known data pattern that is processed in a known manner and may be used at the receiver system to estimate the channel response. The multiplexed pilot and coded data for each data stream is then modulated (i.e., symbol mapped) based on a particular modulation scheme (e.g., BPSK, QPSK, M-PSK, or M-QAM) selected for that data stream to provide modulation symbols. The data rate, coding, and modulation for each data stream may be determined by instructions performed by processor 230.

The modulation symbols for all data streams are then provided to a TX MIMO processor 220, which may further process the modulation symbols (e.g., for OFDM). TX MIMO processor 220 then provides N_(T) modulation symbol streams to N_(T) transmitters (TMTR) 222 a through 222 t. In certain embodiments, TX MIMO processor 220 applies beamforming weights to the symbols of the data streams and to the antenna from which the symbol is being transmitted.

Each transmitter 222 receives and processes a respective symbol stream to provide one or more analog signals, and further conditions (e.g., amplifies, filters, and upconverts) the analog signals to provide a modulated signal suitable for transmission over the MIMO channel. N_(T) modulated signals from transmitters 222 a through 222 t are then transmitted from N_(T) antennas 224 a through 224 t, respectively.

At receiver system 250, the transmitted modulated signals are received by N_(R) antennas 252 a through 252 r and the received signal from each antenna 252 is provided to a respective receiver (RCVR) 254 a through 254 r. Each receiver 254 conditions (e.g., filters, amplifies, and downconverts) a respective received signal, digitizes the conditioned signal to provide samples, and further processes the samples to provide a corresponding “received” symbol stream.

An RX data processor 260 then receives and processes the N_(R) received symbol streams from N_(R) receivers 254 based on a particular receiver processing technique to provide N_(T) “detected” symbol streams. The RX data processor 260 then demodulates, deinterleaves, and decodes each detected symbol stream to recover the traffic data for the data stream. The processing by RX data processor 260 is complementary to that performed by TX MIMO processor 220 and TX data processor 214 at transmitter system 210.

A processor 270 periodically determines which pre-coding matrix to use (discussed below). Processor 270 formulates a reverse link message comprising a matrix index portion and a rank value portion.

The reverse link message may comprise various types of information regarding the communication link and/or the received data stream. The reverse link message is then processed by a TX data processor 238, which also receives traffic data for a number of data streams from a data source 236, modulated by a modulator 280, conditioned by transmitters 254 a through 254 r, and transmitted back to transmitter system 210.

At transmitter system 210, the modulated signals from receiver system 250 are received by antennas 224, conditioned by receivers 222, demodulated by a demodulator 240, and processed by a RX data processor 242 to extract the reserve link message transmitted by the receiver system 250. Processor 230 then determines which pre-coding matrix to use for determining the beamforming weights then processes the extracted message.

Turning to FIG. 3, this figure shows an alternative simplified functional block diagram of a communication device according to one embodiment of the invention. As shown in FIG. 3, the communication device 300 in a wireless communication system can be utilized for realizing the UEs (or ATs) 116 and 122 in FIG. 1, and the wireless communications system is preferably the LTE system. The communication device 300 may include an input device 302, an output device 304, a control circuit 306, a central processing unit (CPU) 308, a memory 310, a program code 312, and a transceiver 314. The control circuit 306 executes the program code 312 in the memory 310 through the CPU 308, thereby controlling an operation of the communications device 300. The communications device 300 can receive signals input by a user through the input device 302, such as a keyboard or keypad, and can output images and sounds through the output device 304, such as a monitor or speakers. The transceiver 314 is used to receive and transmit wireless signals, delivering received signals to the control circuit 306, and outputting signals generated by the control circuit 306 wirelessly.

FIG. 4 is a simplified block diagram of the program code 312 shown in FIG. 3 in accordance with one embodiment of the invention. In this embodiment, the program code 312 includes an application layer 400, a Layer 3 portion 402, and a Layer 2 portion 404, and is coupled to a Layer 1 portion 406. The Layer 3 portion 402 generally performs radio resource control. The Layer 2 portion 404 generally performs link control. The Layer 1 portion 406 generally performs physical connections.

3GPP TS36.321 v11.2.0 states:

5.13 Activation/Deactivation of SCells

If the UE is configured with one or more SCells, the network may activate and deactivate the configured SCells. The PCell is always activated. The network activates and deactivates the SCell(s) by sending the Activation/Deactivation MAC control element described in subclause 6.1.3.8. Furthermore, the UE maintains a sCellDeactivationTimer timer per configured SCell and deactivates the associated SCell upon its expiry. The same initial timer value applies to each instance of the sCellDeactivationTimer and it is configured by RRC. The configured SCells are initially deactivated upon addition and after a handover.

The UE shall for each TTI and for each configured SCell:

-   -   if the UE receives an Activation/Deactivation MAC control         element in this TTI activating the SCell, the UE shall in the         TTI according to the timing defined in [2]:         -   activate the SCell; i.e. apply normal SCell operation             including:             -   SRS transmissions on the SCell;             -   CQI/PMI/RI/PTI reporting for the SCell;             -   PDCCH monitoring on the SCell;             -   PDCCH monitoring for the SCell         -   start or restart the sCellDeactivationTimer associated with             the SCell;     -   else, if the UE receives an Activation/Deactivation MAC control         element in this TTI deactivating the SCell; or     -   if the sCellDeactivationTimer associated with the activated         SCell expires in this TTI:         -   in the TTI according to the timing defined in [2]:             -   deactivate the SCell;             -   stop the sCellDeactivationTimer associated with the                 SCell;             -   flush all HARQ buffers associated with the SCell.     -   if PDCCH on the activated SCell indicates an uplink grant or         downlink assignment; or     -   if PDCCH on the Serving Cell scheduling the activated SCell         indicates an uplink grant or a downlink assignment for the         activated SCell:         -   restart the sCellDeactivationTimer associated with the             SCell;     -   if the SCell is deactivated:         -   not transmit SRS on the SCell;         -   not report CQI/PMI/RI/PTI for the SCell;         -   not transmit on UL-SCH on the SCell;         -   not transmit on RACH on the SCell;         -   not monitor the PDCCH on the SCell;         -   not monitor the PDCCH for the SCell.

NOTE: When SCell is deactivated, the ongoing Random Access procedure on the SCell, if any, is aborted.

Furthermore, 3GPP TR 36.392 v12.0.0 states:

Small cells using low power nodes are considered promising to cope with mobile traffic explosion, especially for hotspot deployments in indoor and outdoor scenarios. A low-power node generally means a node whose Tx power is lower than macro node and BS classes, for example Pico and Femto eNB are both applicable. Small cell enhancements for E-UTRA and E-UTRAN will focus on additional functionalities for enhanced performance in hotspot areas for indoor and outdoor using low power nodes.

This document captures the scenarios and requirements for small cell enhancements. 3GPP TR 36.913 [3] should be used as reference whenever applicable in order to avoid duplication of the requirements.

In addition, 3GPP RP-122033 states:

4 Objective *

The objective of this study is to identify potential technologies in the protocol and architecture for enhanced support of small cell deployment and operation which should satisfy scenarios and requirements defined in TR 36.932.

The study shall be conducted on the following aspects:

-   -   Identify and evaluate the benefits of UEs having dual         connectivity to macro and small cell layers served by different         or same carrier and for which scenarios such dual connectivity         is feasible and beneficial.     -   Identify and evaluate potential architecture and protocol         enhancements for the scenarios in TR 36.932 and in particular         for the feasible scenario of dual connectivity and minimize core         network impacts if feasible, including:         -   Overall structure of control and user plane and their             relation to each other, e.g., supporting C-plane and U-plane             in different nodes, termination of different protocol             layers, etc.     -   Identify and evaluate the necessity of overall Radio Resource         Management structure and mobility enhancements for small cell         deployments:         -   Mobility mechanisms for minimizing inter-node UE context             transfer and signalling towards the core network.         -   Measurement and cell identification enhancements while             minimizing increased UE battery consumption.

For each potential enhancement, the gain, complexity and specification impact should be assessed.

The study shall focus on potential enhancements which are not covered by other SI/WIs.

Also, 3GPP TS 36.300 V11.4.0 provides the following the description regarding Carrier Aggregation (CA):

5.5 Carrier Aggregation

In Carrier Aggregation (CA), two or more Component Carriers (CCs) are aggregated in order to support wider transmission bandwidths up to 100 MHz. A UE may simultaneously receive or transmit on one or multiple CCs depending on its capabilities:

-   -   A UE with single timing advance capability for CA can         simultaneously receive and/or transmit on multiple CCs         corresponding to multiple serving cells sharing the same timing         advance (multiple serving cells grouped in one TAG);     -   A UE with multiple timing advance capability for CA can         simultaneously receive and/or transmit on multiple CCs         corresponding to multiple serving cells with different timing         advances (multiple serving cells grouped in multiple TAGs).         E-UTRAN ensures that each TAG contains at least one serving         cell;     -   A non-CA capable UE can receive on a single CC and transmit on a         single CC corresponding to one serving cell only (one serving         cell in one TAG).

CA is supported for both contiguous and non-contiguous CCs with each CC limited to a maximum of 110 Resource Blocks in the frequency domain using the Rel-8/9 numerology.

It is possible to configure a UE to aggregate a different number of CCs originating from the same eNB and of possibly different bandwidths in the UL and the DL:

-   -   The number of DL CCs that can be configured depends on the DL         aggregation capability of the UE;     -   The number of UL CCs that can be configured depends on the UL         aggregation capability of the UE;     -   It is not possible to configure a UE with more UL CCs than DL         CCs;     -   In typical TDD deployments, the number of CCs and the bandwidth         of each CC in UL and DL is the same.     -   The number of TAGs that can be configured depends on the TAG         capability of the UE.

CCs originating from the same eNB need not to provide the same coverage.

CCs shall be LTE Rel-8/9 compatible. Nevertheless, existing mechanisms (e.g. barring) may be used to avoid Rel-8/9 UEs to camp on a CC.

The spacing between centre frequencies of contiguously aggregated CCs shall be a multiple of 300 kHz. This is in order to be compatible with the 100 kHz frequency raster of Rel-8/9 and at the same time preserve orthogonality of the subcarriers with 15 kHz spacing. Depending on the aggregation scenario, the n×300 kHz spacing can be facilitated by insertion of a low number of unused subcarriers between contiguous CCs.

[ . . . ]

7.5 Carrier Aggregation

When CA is configured, the UE only has one RRC connection with the network. At RRC connection establishment/re-establishment/handover, one serving cell provides the NAS mobility information (e.g. TAI), and at RRC connection re-establishment/handover, one serving cell provides the security input. This cell is referred to as the Primary Cell (PCell). In the downlink, the carrier corresponding to the PCell is the Downlink Primary Component Carrier (DL PCC) while in the uplink it is the Uplink Primary Component Carrier (UL PCC).

Depending on UE capabilities, Secondary Cells (SCells) can be configured to form together with the PCell a set of serving cells. In the downlink, the carrier corresponding to an SCell is a Downlink Secondary Component Carrier (DL SCC) while in the uplink it is an Uplink Secondary Component Carrier (UL SCC).

The configured set of serving cells for a UE therefore always consists of one PCell and one or more SCells:

-   -   For each SCell the usage of uplink resources by the UE in         addition to the downlink ones is configurable (the number of DL         SCCs configured is therefore always larger than or equal to the         number of UL SCCs and no SCell can be configured for usage of         uplink resources only);     -   From a UE viewpoint, each uplink resource only belongs to one         serving cell;     -   The number of serving cells that can be configured depends on         the aggregation capability of the UE (see subclause 5.5);     -   PCell can only be changed with handover procedure (i.e. with         security key change and RACH procedure);     -   PCell is used for transmission of PUCCH;     -   Unlike SCells, PCell cannot be de-activated (see subclause         11.2);     -   Re-establishment is triggered when PCell experiences RLF, not         when SCells experience RLF;     -   NAS information is taken from PCell.

The reconfiguration, addition and removal of SCells can be performed by RRC. At intra-LTE handover, RRC can also add, remove, or reconfigure SCells for usage with the target PCell. When adding a new SCell, dedicated RRC signalling is used for sending all required system information of the SCell i.e. while in connected mode, UEs need not acquire broadcasted system information directly from the SCells.

In addition, 3GPP TS 36.331 V11.3.0 provides the following description:

5.3.10.3b SCell Addition/Modification

The UE shall:

-   -   for each sCellIndex value included in the sCellToAddModList that         is not part of the current UE configuration (SCell addition):         -   add the SCell, corresponding to the cellIdentification, in             accordance with the received radioResourceConfigCommonSCell             and radioResourceConfigDedicatedSCell;         -   configure lower layers to consider the SCell to be in             deactivated state;     -   for each sCellIndex value included in the sCellToAddModList that         is part of the current UE configuration (SCell modification):         -   modify the SCell configuration in accordance with the             received radioResourceConfigDedicatedSCell;

During discussion on Rel-10 carrier aggregation in RAN2#72 (as discussed in 3GPP R2-110679), it was generally concluded that Radio Link Monitoring (RLM) on SCell (Secondary Cell) was not needed and would rely on network control. For example, the eNB (evolved Node B) can determine the link status of an SCell based on the CQI (Channel Quality Indicator) report from the UE.

If separate eNBs are adopted for supporting dual connectivity, the small cell eNB could determine the link status of the small cell from the CQI report, and could forward the link status to the macro eNB when necessary (such as, upon radio link failure) so that the macro eNB could take action (such as deactivating and/or removing the small cell) to remedy the situation. However, the action would be delayed due to non-ideal backhaul (max. 60 ms, as discussed in 3GPP TR 36.392 V 12.0.0), which would postpone the subsequent data transfer of the radio bearers allocated to the small cell eNB. The delay could be critical because the data allocated to the small cell eNB could not be transferred via the macro cell.

In general, to eliminate the postponement or delay of the subsequent data transfer of the radio bearers allocated to the small cell eNB, a potential solution would be for the UE to monitor the radio link with the small cell and report a radio link failure to the macro eNB when the radio link failure is detected on the small cell.

In one embodiment, the UE could further stop uplink transmission to the small cell for avoiding interference to other transmissions. Alternatively, the UE could deactivate the small cell to stop both uplink transmissions and PDCCH (Physical Downlink Control Channel) monitoring. In other embodiments, the radio link failure could be detected based on to “out-of-sync” and “in-sync” indications from a physical layer and a timer. Alternatively, the radio link failure could be detected due to a random access problem on the small cell.

FIG. 5 is a flow chart 500 for monitoring a radio link on a small cell from the perspective of a UE in a wireless communication system in accordance with one exemplary embodiment. In this embodiment, the UE is served by a first cell controlled by a first eNB (evolved Node B). In step 505, the UE receives a RRC (Radio Resource Control) message for configuring a second cell to the UE. In one embodiment, the RRC message for configuring the second cell to the UE is an RRC Connection Reconfiguration message received from the first eNB.

In step 510, the UE transmits a complete message in response to the RRC message for configuring the second cell. In step 515, if the second cell is controlled by a second eNB, the UE would monitor a radio link with the second cell and would report a radio link failure to the first eNB when the radio link failure is detected on the second cell. In one embodiment, if the second cell is controlled by the first eNB, the UE does not monitor the radio link with the second cell and does not report the radio link failure to the first eNB.

In one embodiment, the radio link failure could be detected based on “out-of-sync” and “in-sync” indications from a physical layer and a timer. Furthermore, the radio link failure could be detected due to a random access problem on the second cell. In addition, the radio link failure could be reported via a RRC signaling or an MAC (Medium Access Control) signaling

In one embodiment, the UE could stop uplink transmission(s) to the second cell after detection of the radio link failure, as shown in step 520. In another embodiment, the UE could deactivate the second cell after detection of the radio link failure.

Referring back to FIGS. 3 and 4, in one embodiment, the device 300 could include a program code 312 stored in memory 310 for monitoring a radio link on a small cell in a wireless communication system, wherein a UE is served by a first cell controlled by a first eNB. The CPU 308 could execute the program code 312 to enable the UE (i) to receive a RRC message for configuring a second cell to the UE, (ii) to transmit a complete message in response to the RRC message for configuring the second cell, and (iii) to monitor a radio link with the second cell and reports a radio link failure to the first eNB when the radio link failure is detected on the second cell, if the second cell is controlled by a second eNB. In one embodiment, if the second cell is controlled by the first eNB, the UE would not monitor the radio link with the second cell and would not report the radio link failure to the first eNB.

In one embodiment, the CPU 308 could furthermore execute the program code 312 to enable the UE (i) to stop uplink transmission(s) to the second cell after detection of the radio link failure, and/or (ii) to deactivate the second cell after detection of the radio link failure. In addition, the CPU 308 could execute the program code 312 to perform all of the above-described actions and steps or others described herein.

FIG. 6 is a flow chart 600 for monitoring a radio link on a small cell from the perspective of an eNB (evolved Node B) in a wireless communication system in accordance with one exemplary embodiment. In this embodiment, the UE is served by a first cell controlled by a first eNB. In step 605, the first eNB transmits a RRC message for configuring a second cell to the UE. In one embodiment, the RRC message for configuring the second cell to the UE is an RRC Connection Reconfiguration message.

In step 610, the first eNB receives a complete message from the UE in response to the RRC message for configuring the second cell. In step 615, if the second cell is controlled by a second eNB, the first eNB would receive a radio link failure report on the second cell from the UE. In one embodiment, if the second cell is controlled by the first eNB, the first eNB would not receive the radio link failure report on the second cell from the UE. In one embodiment, the radio link failure could be detected based on “out-of-sync” and “in-sync” indications from a physical layer and a timer. Furthermore, the radio link failure could be detected due to a random access problem on the second cell. In addition, the radio link failure could be reported via a RRC signaling or an MAC (Medium Access Control) signaling.

In one embodiment, as shown in step 620, the first eNB could transmit another RRC message to the UE to remove the second cell after reception of the radio link failure report.

Referring back to FIGS. 3 and 4, in one embodiment, the device 300 could include a program code 312 stored in memory 310 for monitoring a radio link on a small cell in a wireless communication system, wherein a UE is served by a first cell controlled by a first eNB. The CPU 308 could execute the program code 312 to enable the first eNB (i) to transmit a RRC message for configuring a second cell to the UE, (ii) to receive a complete message from the UE in response to the RRC message for configuring the second cell, and (iii) to receive a radio link failure report on the second cell from the UE if the second cell is controlled by a second eNB. In one embodiment, if the second cell is controlled by the first eNB, the first eNB would not receive the radio link failure report on the second cell from the UE.

In one embodiment, the CPU 308 could execute the program code 312 to enable the first eNB to transmit another RRC message to the UE to remove the second cell after reception of the radio link failure report. In addition, the CPU 308 could execute the program code 312 to perform all of the above-described actions and steps or others described herein.

Various aspects of the disclosure have been described above. It should be apparent that the teachings herein may be embodied in a wide variety of forms and that any specific structure, function, or both being disclosed herein is merely representative. Based on the teachings herein one skilled in the art should appreciate that an aspect disclosed herein may be implemented independently of any other aspects and that two or more of these aspects may be combined in various ways. For example, an apparatus may be implemented or a method may be practiced using any number of the aspects set forth herein. In addition, such an apparatus may be implemented or such a method may be practiced using other structure, functionality, or structure and functionality in addition to or other than one or more of the aspects set forth herein. As an example of some of the above concepts, in some aspects concurrent channels may be established based on pulse repetition frequencies. In some aspects concurrent channels may be established based on pulse position or offsets. In some aspects concurrent channels may be established based on time hopping sequences. In some aspects concurrent channels may be established based on pulse repetition frequencies, pulse positions or offsets, and time hopping sequences.

Those of skill in the art would understand that information and signals may be represented using any of a variety of different technologies and techniques. For example, data, instructions, commands, information, signals, bits, symbols, and chips that may be referenced throughout the above description may be represented by voltages, currents, electromagnetic waves, magnetic fields or particles, optical fields or particles, or any combination thereof.

Those of skill would further appreciate that the various illustrative logical blocks, modules, processors, means, circuits, and algorithm steps described in connection with the aspects disclosed herein may be implemented as electronic hardware (e.g., a digital implementation, an analog implementation, or a combination of the two, which may be designed using source coding or some other technique), various forms of program or design code incorporating instructions (which may be referred to herein, for convenience, as “software” or a “software module”), or combinations of both. To clearly illustrate this interchangeability of hardware and software, various illustrative components, blocks, modules, circuits, and steps have been described above generally in terms of their functionality. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present disclosure.

In addition, the various illustrative logical blocks, modules, and circuits described in connection with the aspects disclosed herein may be implemented within or performed by an integrated circuit (“IC”), an access terminal, or an access point. The IC may comprise a general purpose processor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, electrical components, optical components, mechanical components, or any combination thereof designed to perform the functions described herein, and may execute codes or instructions that reside within the IC, outside of the IC, or both. A general purpose processor may be a microprocessor, but in the alternative, the processor may be any conventional processor, controller, microcontroller, or state machine. A processor may also be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration.

It is understood that any specific order or hierarchy of steps in any disclosed process is an example of a sample approach. Based upon design preferences, it is understood that the specific order or hierarchy of steps in the processes may be rearranged while remaining within the scope of the present disclosure. The accompanying method claims present elements of the various steps in a sample order, and are not meant to be limited to the specific order or hierarchy presented.

The steps of a method or algorithm described in connection with the aspects disclosed herein may be embodied directly in hardware, in a software module executed by a processor, or in a combination of the two. A software module (e.g., including executable instructions and related data) and other data may reside in a data memory such as RAM memory, flash memory, ROM memory, EPROM memory, EEPROM memory, registers, a hard disk, a removable disk, a CD-ROM, or any other form of computer-readable storage medium known in the art. A sample storage medium may be coupled to a machine such as, for example, a computer/processor (which may be referred to herein, for convenience, as a “processor”) such the processor can read information (e.g., code) from and write information to the storage medium. A sample storage medium may be integral to the processor. The processor and the storage medium may reside in an ASIC. The ASIC may reside in user equipment. In the alternative, the processor and the storage medium may reside as discrete components in user equipment. Moreover, in some aspects any suitable computer-program product may comprise a computer-readable medium comprising codes relating to one or more of the aspects of the disclosure. In some aspects a computer program product may comprise packaging materials.

While the invention has been described in connection with various aspects, it will be understood that the invention is capable of further modifications. This application is intended to cover any variations, uses or adaptation of the invention following, in general, the principles of the invention, and including such departures from the present disclosure as come within the known and customary practice within the art to which the invention pertains. 

What is claimed is:
 1. A method for monitoring a radio link on a small cell in a wireless communication system, wherein a UE (User Equipment) is served by a first cell controlled by a first eNB (evolved Node B), comprising: the UE receives a RRC (Radio Resource Control) message for configuring a second cell to the UE; the UE transmits a complete message in response to the RRC message for configuring the second cell; and the UE monitors a radio link with the second cell and reports a radio link failure to the first eNB when the radio link failure is detected on the second cell, if the second cell is controlled by a second eNB.
 2. The method of claim 1, wherein the UE does not monitor the radio link with the second cell and does not report the radio link failure to the first eNB if the second cell is controlled by the first eNB.
 3. The method of claim 1, further comprising: the UE stops uplink transmission(s) to the second cell after detection of the radio link failure.
 4. The method of claim 1, further comprising: the UE deactivates the second cell after detection of the radio link failure.
 5. The method of claim 1, wherein the radio link failure is detected based on “out-of-sync” and “in-sync” indications from a physical layer and a timer, or is detected due to a random access problem on the second cell.
 6. The method of claim 1, wherein the radio link failure is reported via a RRC signaling or an MAC (Medium Access Control) signaling.
 7. The method of claim 1, wherein the RRC message for configuring the second cell to the UE is an RRC Connection Reconfiguration message received from the first eNB.
 8. A method for monitoring a radio link on a small cell in a wireless communication system, wherein a UE (User Equipment) is served by a first cell controlled by a first eNB (evolved Node B), comprising: the first eNB transmits a RRC (Radio Resource Control) message for configuring a second cell to the UE; the first eNB receives a complete message from the UE in response to the RRC message for configuring the second cell; and the first eNB receives a radio link failure report on the second cell from the UE if the second cell is controlled by a second eNB.
 9. The method of claim 8, wherein the first eNB does not receive the radio link failure report on the second cell from the UE if the second cell is controlled by the first eNB.
 10. The method of claim 8, further comprising: the first eNB transmits another RRC message to the UE to remove the second cell after reception of the radio link failure report.
 11. The method of claim 8, wherein the radio link failure is detected based on “out-of-sync” and “in-sync” indications from a physical layer and a timer, or is detected due to a random access problem on the second cell.
 12. The method of claim 8, wherein the radio link failure is reported via a RRC signaling or an MAC (Medium Access Control) signaling.
 13. The method of claim 8, wherein the RRC message for configuring the second cell to the UE is an RRC Connection Reconfiguration message.
 14. A communication device for monitoring a radio link on a small cell in a wireless communication system, wherein a UE (User Equipment) is served by a first cell controlled by a first eNB (evolved Node B), the communication device comprising: a control circuit; a processor installed in the control circuit; a memory installed in the control circuit and operatively coupled to the processor; wherein the processor is configured to execute a program code stored in memory to enable the UE to: receive a RRC (Radio Resource Control) message for configuring a second cell to the UE; transmit a complete message in response to the RRC message for configuring the second cell; and monitor a radio link with the second cell and reports a radio link failure to the first eNB when the radio link failure is detected on the second cell, if the second cell is controlled by a second eNB.
 15. The communication device of claim 14, wherein the UE does not monitor the radio link with the second cell and does not report the radio link failure to the first eNB if the second cell is controlled by the first eNB.
 16. The communication device of claim 14, wherein the processor is further configured to execute a program code stored in memory to enable the UE to stop uplink transmission(s) to the second cell after detection of the radio link failure.
 17. The communication device of claim 14, wherein the processor is further configured to execute a program code stored in memory to enable the UE to deactivate the second cell after detection of the radio link failure.
 18. The communication device of claim 14, wherein the radio link failure is detected based on “out-of-sync” and “in-sync” indications from a physical layer and a timer, or is detected due to a random access problem on the second cell.
 19. The communication device of claim 14, wherein the radio link failure is reported via a RRC signaling or an MAC (Medium Access Control) signaling.
 20. The communication device of claim 14, wherein the RRC message for configuring the second cell to the UE is an RRC Connection Reconfiguration message received from the first eNB. 